Terraced Craters in Aitken Crater

Small crater within Aitken crater. It has a terraced and hummocky floor, with boulders strewn about, and no bright rays. NAC image M145855135RE, image width is 700 m [NASA/GSFC/Arizona State University].

This crater has an unusual floor for its size. An impact crater of this size typically has a simple bowl shape, yet this example displays terraces and hummocks. The terraces give us insight into the impact material. A bolide that impacts a solid surface covered by loose material, for example mare covered by regolith, will use less of its energy to break up the loose material than solid material. The "excess" energy goes into excavating more material thus making for a larger diameter. Thus we see terrace at the boundary between the regolith and underlying more coherent material. The fact that the crater has no bright rays indicates that it is old - its rays have weathered into the background.

Location of the terraced crater within Aitken crater. Image width is 160 km [NASA/GSFC/Arizona State University].